Atomic Force Microscopy Techniques for Nanomechanical Characterization: A Polymeric Case Study

Abstract

Atomic force microscopy (AFM) is a versatile tool to perform mechanical\ud characterization of surface samples at the nanoscale. In this work, we review\ud two of such methods, namely contact resonance AFM (CR-AFM) and torsional\ud harmonics AFM (TH-AFM). First, such techniques are illustrated and their\ud applicability on materials with elastic moduli in different ranges are discussed,\ud together with their main advantages and limitations. Then, a case\ud study is presented in which we report the mechanical characterization using\ud both CR-AFM and TH-AFM of polyaniline and polyaniniline doped with\ud nanodiamond particles tablets prepared by a pressing process. We determined\ud the indentation modulus values of their surfaces, which were found in fairly\ud good agreement, thus demonstrating the accuracy of the techniques. Finally,\ud the determined surface elastic moduli have been compared with the bulk ones\ud measured through standard indentation testin

Contact resonance atomic force microscopy for viscoelastic characterization of polymer-based nanocomposites at variable temperature

“…The values of r we obtained were found to slightly vary among different measurements, doing range between 0.93 and 0.98. These values are in any case lower than the real value of r = 0.985 determined by scanning electron microscopy (SEM) images [25]. This can be attributed to the fact that lateral forces at the tip-sample contact increase the CRFs associated to each mode at relatively large values of k * /k c [44].…”

“…A commercial blend of polystyrene (PS) and low-density polyethylene (LDPE) on Si substrate (PS/LDPE, Bruker Inc.) was used to assess the accuracy of the technique at room temperature [15,25]. LDPE and polycarbonate (PC) sheets 1 mm thick (Goodfellow Cambridge Ltd.) were used as reference samples to verify the accuracy of CR-AFM for viscoelastic characterizations [26,27].…”

Elastic modulus measurements at variable temperature: Validation of atomic force microscopy techniques

“…In order to perform CR-AFM measurements, first we measured the first two free resonance frequencies of each cantilever, typical values of which were f 0 1 = 25 kHz and f 0 2 = 130 kHz. These values were used to calibrate the characteristic geometrical constants of the cantilevers, as detailed elsewhere [43][44][45][46]. In the second step of the CR-AFM experimental procedure the first two CRFs were acquired.…”

Mechanical Characterization of Methanol Plasma Treated Fluorocarbon Ultrathin Films Through Atomic Force Microscopy

“…The AFM setup was equipped with a Si cantilever (CSG10, NT-MDT, Russia) with spring constant k c = 0.116 N/m, determined through the method described by Sader et al (1999). In order to evaluate the instrumental parameters required to analyze CR-AFM data, a well-established experimental procedure was followed (Reggente et al, 2015): standard force-deflection curves have been acquired on Si (100) single crystal to calibrate the cantilever force sensitivity; tip radius R t has been evaluated by reconstructing the tip shape through the analysis of the images collected on an array of inverted tips used as reference sample (TGZ1, NT-MDT, Russia); the exact position of the tip along the cantilever axis has been determined through scanning electron microscopy (SEM) analysis. Being the tip in contact with the sample surface, contact resonance frequencies (CRFs) were detected for each sample and CRFs values and the corresponding uncertainties have been evaluated from statistics performed on not <512 points of CR-AFM images.…”